Anatomy of the Eye Flashcards by Shahana Sengupta

What are the 6 oculomotor muscles that allow rotation of the ocular bulb?

lateral rectus: outward horizontal movement
median rectus: horizontal movement towards medial line of body
superior rectus: upward movement
inferior rectus: downward movement
inferior oblique: downward outer rotation
superior oblique: upward external rotation

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How are the eyes connected to the encephalon (brain)?

via the optic nerves

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What are the 3 fluid filled spaces within an eye?

ANTERIOR CHAMBER
Located between cornea and iris.
Contains aqueous humour.

POSTERIOR CHAMBER
Located between iris and lens.
Contains aqueous humour.

VITREOUS CHAMBER
Located posterior to the lens, between the lens and the posterior wall/retina of the eye
Contains vitreous humour.

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What are the components of the ‘outer fibrous tunic’ of the eye?

= external membrane, which is divided into”

CORNEA: anterior aspect, which lacks blood vessels and lymphatic vessels.
SCLERA: posterior aspect. Poorly vascularised

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What is the palpebral fissure?

oval shaped space between the medial and lateral canthi of the eye lids

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How does the upper eye lid differ to the lower lid?

bigger

- more mobile

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What are the medial and lateral canthi?

corners of the eye lids

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What is lacrimal caruncle?

globular nodule at the medial canthus

made of skin covering sebaceous and sweat glands

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What is the location and function of the lacrimal gland?

located near the lateral canthus superiorly

it is where tears are produced and secreted to the surface of the globe via the lacrimal dict

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What is the lacrimal papilla?

small, fleshy projection of the margin of each eyelid close to the medial canthus
Opening of the papilla: PUNCTUM

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What is the function of the lacrimal punctum?

opening of the papilla

where tears are collected and travel through the superior and inferior lacrimal canaliculi to the lacrimal sac

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Where does the lacrimal sac drain to?

contains tears

drains to the inferior nasal meatus through the naso-lacrimal duct (“runny nose”)

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Where is the tough sclera located?

part of the fibrous layer of the globe

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Why might loss of sympathetic innervation cause mild drooping (ptosis) of the eyelid?

Ptosis is mild as innervation only lost to the smooth muscle aspect of LEVATOR PALPEBRAE SUPERIORIS muscle
(~30% of its fibres)

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What is the other name for the Levator superioris muscle?

Müller’s muscle

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Why might more of the sclera be visible during anxiety or in hyperthyroidism?

increased activity in Müller’s muscle via the sympathetic fibre (stimulation)
=> wide eyes

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What is the bony orbit?

dry skull

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Which bones are contained within the bony orbit?

frontal
zygomatic
maxillary
lacrimal
ethmoid
sphenoid

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What does the optic canal transmit?

CN II (optic nerve)

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What does the superior orbital fissure transmit?

CN III (oculomotor nerve)
CN IV (trochlear nerve) 
CN V1 (branch one of trigeminal nerve: ophthalmic nerve)
CN VI (abducens nerve)

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What are the 12 cranial nerves?

OLFACTORY (CN I)

OPTIC (CN II)

OCULOMOTOR (CN III)

TROCHLEAR (CN IV)

TRIGEMINAL (CN V)

ABDUCENS (CN VI)

FACIAL (CN VII)

VESTIBULOCOCHLEAR (CN VIII)

GLOSSOPHARYNGEAL (CN IX)

VAGUS (CN X)

ACCESSORY NERVE (CN XI)

HYPOGLOSSAL (CN XII)

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How many degrees does the eye need to be adducted by in order for the visual and anatomical axes to coincide?

pupil needs to be adducted at ~22.5 degrees

this is from its neural position to make the visual axis (line of sight) coincide with the anatomical axis

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What is an orbital “blowout” fracture?

usually follows energetic impact to the anterior globe

this causes a sharp increase in infraorbital pressure
fracturing the thin bony plates of the orbital walls

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What is the globe of the eye surrounded by?

periorbital fat

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What are the 3 layers of the eye?

- fibrous - vascular - neural

what is the outer layer of the eye composed of?

tough, collagen-rich fibrous tissue

What makes up the outer layer of the eye?

(fibrous tunic = outer layer) - sclera - cornea

What is the cornea?

a transparent, protective layer covering the iris and pupil

What is the fibrous tunic layer continuous with ?

the dural sheet - covers the optic nerve

where the optic nerve emerge from the globe?

the posterior-medial aspect of the globe

What are the components of the vascular tunic?

- choroid - ciliary body - iris

What is the function of the choroid?

provides O2 and nourishment to the outer layers of the retina

What is the function of the ciliary body?

CILIARY MUSCLE controls the shape of the lens CILIARY EPITHELIUM produces the aqueous humour

What is the function of the iris?

controls the diameter and size of the pupil | and therefore the amount of light reaching the retina

What dos the uveal tract refer to?

components of the vascular tunic (choroid, iris, and ciliary body)

What is the importance of the pigmentation within the choroid?

melanin helps the choroid to limit uncontrolled reflection whin the eye this would result in perception of confusing images

What is the function of the retina?

receives light that the lens has focused | then converts the light into neural signals and sends them to the brain for interpretation

What is the macula lutea?

= yellow spot FOVEA: contained within the macula is a small central pit used for central vision like reading - important for high acuity, central vision

Where is the physiological blind spot?

at the optic nerve head (optic disc)

What type of photoreceptors are usually affected to affect night vision?

=> Rods night blindness: nyctalopia (usually occurs due to retinitis pigmentosa)

What are RODS important for?

- work well in low-light (scotopic) - important for night vision - more important for peripheral vision - detection of moving objects

What are CONES important for?

- in stronger light (photopic) - provide colour vision - for fine details (e.g. reading) - much more abundant in the central area of retina

Where are CONES most numerous?

central retina: - macular lutea - fovea centralis

What is uveitis?

inflammation of the uveal tract

What is irodocyclitis?

inflammation of iris and the ciliary body inflammation is predominately confined to the ciliary body

Where is the lens located?

nestled in the hyaloid fossa | bowl shaped depression in the anterior surface of the vitreous body

What is the vitreous body?

clear gel that fills the space between the lens and the retina

How do the anterior and posterior curvatures of the lens differ?

anterior surface is less curved that the posterior

What causes flattening of the anterior surface of the lens?

tension in the ciliary zonule

What is the length of the normal eye in adulthood?

24 mm

How does myopia relate to eye length?

short sightedness die to a long eyeball (>24mm)

What is the nature of aqueous humour?

- similar to blood plasma - but with low protein concentration - helps to maintain the intraocular pressure - maintains spherical shape of the eye

Where is aqueous humour reabsorbed?

the sinus venosus | = canal of Schlemm

What is the normal intraocular pressure?

~ 16-21 mmHg

What the fundus of the eye refer to?

back of the inside of the eye | includes the retina and optic nerve

What feature seen on fundoscopy would suggest raised intraocular pressure?

enlargement of the optic cup (cup-like hole in middle of optic disc)

What is the clinical significance of the cup-to-disc ration in eye disease?

measure of used in Dx of glaucoma

How do fibres from the retina travel to the optic chiasm?

fibres from the nasal/inside half of each retina cross to the opposite side of the optic chiasm this means that info from the RHS of the visual field goes to the LHS of the brain (+vice versa)

If a patient has a right sided hemianopia, how is the lesion located relative to the optic chiasm?

= field defect lesion must be posterior to the optic chiasm only a problem localised to one eye (monocular visual defect) can be located anterior to the chiasm

What does the trochlear nerve supply?

only the superior oblique muscle | therefore nerve is v. thin

Where does the abducens nerve arise?

between the pons and medullary pyramid

What kind of innervation does the oculomotor provide?

PNS innervation to the eye

Which 2 structures receive PNS stimulation from the oculomotor nerve?

SPHINCTER PUPILLAE constricts the pupil, reducing the amount of light entering the eye CILIARY MUSCLES contracts causing the lens to become more spherical (better for short distance vision)

What are the 2 pupil reflexes of the eye?

- light reflex | - near reflex

What 3 components make up the accommodation reflex?

- pupillary constriction - medial convergence of the eyes - focusing of the eyes on a near object (required contraction of ciliary muscles and bulging of the lens)

Which muscles cause medial convergence of the eyes?

medial recti muscles

Why is a sudden dilation of one pupil a concern in someone with a head injury?

oculomotor nerve is closely related to the free edge of the tentorium this can get compressed the PNS fibres (pupilloconstrictor) are locals at the peripheral part of this nerve -> pupil size is affected

What are the 2 main types of third nerve palsy?

Third nerve = CN III = oculomotor nerve - SURGICAL: due to mechanical compression - MEDICAL (diabetic for e.g.) causes ischaemia this is pupil sparing - since the pupilloconstcitr fibres are at the periphery and therefore better perfused unlike the oculomotor at fibres located centrally